1. Field of the Invention
The present invention relates in general to apparatus for feeding sheets of paper or the like sequentially from a stack. More particularly, the present invention relates to an improved apparatus wherein sheets of paper are fed from the top of a stack of sheets and stack at the bottom of the stack.
2. Prior Art
Many different types of sheet feeding machines are available in the prior art. The sheet feeding machines are generally used in combination with electrophotographic copying machines, printing machines, multigraph machines, collators, etc.
In one type of prior art sheet feeding machines, sheets are fed from the bottom of a stack while sheet stacking (i.e, the addition of sheets) occurs on top. This type of sheet stacking machine is generically called "Top Stacking, Bottom Feeding" sheet feeding machines.
U.S. Pat. No. 3,385,593 is representative of the top stacking bottom feed prior art sheet feeding machines. In this type of sheet feeding machine a stack of sheets is supported by a support mechanism having an opening in its bottom surface to expose a portion of the bottom sheet in the stack. The end of the stack adjoining the opening is further supported by a bracket member. The support mechanism is fitted with pneumatic means which help to support the sheets in the support mechanism. A reciprocable motion-transmitting member is mounted directly beneath the support mechanism. The reciprocating motion occurs in a horizontal plane which runs parallel to the bottom surface of the support mechanism. The reciprocable motion transmitting member is also activated upwardly and downwardly with respect to the plane of reciprocable motion. All motions, be it reciprocable, upward or downward, are generated from a rotatable cam roller motor assembly. A vacuum assisted picker member is mounted on the reciprocable motion-transmitting member. The picker member is positioned to be in alignment with the opening in the support mechanism.
In operation, the picker member under the control of the rotatable cam-roller motor assembly moves into contact with the bottom sheet in the stack. The picker member moves backward, so as to release the sheet from the bracket member, downward and then forward to deliver the sheet. A more detailed description of this type of prior art sheet feeding machine is given in the above referenced U.S. Patent.
U.S. Pat. No. Re. 27,976 is another example of prior art bottom feed top stacking prior art sheet feeding machine. In the patent, sheets are fed sequentially from a sheet support bin or tray. The tray consists of a bottom wall with a plurality of continguous side walls. A rotatable drive roller protrudes through a hole in the bottom wall to drive a sheet through an opening in one of the side walls. In order to maintain pressure on the stack of sheets positioned in the tray an adjustable spring loaded weight is positioned to move relative to the bottom wall of said tray.
In another type of prior art sheet feeding device a sheet is fed from the top of a stack of sheets while sheets are added to the stack from the top. Generically, this type of prior art sheet feeding device can be classified as the Top Stacking Top Feeding. In this type of sheet feeding device by necessity the stacking and feeding functions occur sequentially.
When the above described prior art sheet feeding machines are adopted for use as a recirculating document feed, particularly in conjunction with an electrophotographic machine at least two of the above described units are needed. A particular configuration showing the use of the bottom feed top stacking unit as a recirculating document feed is shown in the above described U.S. Pat. No. Re. 27,976. In the configuration the document glass of the electrophotographic machine is positioned between a pair of the above described bottom feed top stacking units. The bottom feed top stacking units are integrally formed with the electrophotographic machine. As such there is a lack of modularity between the units and the electrophotographic machine. The lack of modularity is an undesirable result.
Another drawback with the above configuration is that it is relatively expensive and cumbersome due to the fact that two units are needed for the recirculating document feed. One of the units is needed to deliver a sheet on the document glass and another unit is needed to accept the sheet after processing. Even where the unit is not used in the environment of a recirculating document feed but is used as a sequential paper feed device, one unit cannot be used as a stacker and feeder simultaneously. As such there are several limitations in the prior art sheet feeding units which the present invention will alleviate.
Another problem which is associated with top stacking paper feed devices is that these devices have relatively low reliability. The low reliability stems from the fact that the stacking occurs on a pile or stack whose height changes periodically. This requires either a stacking mechanism which adjusts its throw on the stack, as the height of the stack changes, or a constant throw stacker which throws at a height to clear the top of the stack. Either way precise control of the stacking mechanism is necessary to assure proper operation. The control means which is needed to maintain precise control over the stacking mechanism tends to increase the complexity of the device and hence a reduction in its reliability.